5aNS1. Crosswind effects on acoustic propagation.

Ray theory says that a ray moving in a crosswind will drift out of the
plane of propagation, and that this effect can be significant with high
windspeeds and over long propagation distances. White and Li [Michael J. White
and Y. L. Li, J. Acoust. Soc. Am. 92, 2405 (A) (1992)] and Wilson [D. Keith
Wilson, J. Acoust. Soc. Am. 92, 2405 (A) (1992)] developed two-dimensional
fast-field programs (2DFFPs) to calculate the sound pressure levels of windy
atmospheres. They reported that crosswind effects were negligible for the cases
they considered and that a one-dimensional stationary phase solution yields
accurate results. Ray analysis of the two-dimensional phase space used in the
2DFFP indicates that there is a small region that contributes significantly to
the sound level. In the presence of a crosswind, the one-dimensional stationary
phase approximation does not include all of this region. 2DFFP calculations for
realistic windspeeds that show crosswind drift are presented, and the 2DFFP
calculations are compared to the calculations of a one-dimensional stationary
phase approximation.